1. Field of the Disclosure
The present disclosure relates generally to wireless charging and, more particularly, to a method for transmitting wireless power in a wireless charging system including a wireless power transmitting unit and a wireless power receiving unit.
2. Description of the Related Art
Mobile terminals such as a mobile phone, a personal digital assistant (PDA) and the like are configured for use with rechargeable batteries due to their nature, and the battery of the mobile terminal is charged through supplied electronic energy by using a separate charging apparatus. Typically, the charging device and the battery have separate contact terminals at an exterior thereof and are electrically connected to each other by contact between the contact terminals.
However, in such a contact-type charging scheme, the contact terminals protrude outwardly, and thus are easily contaminated by foreign substances or exposed to moisture. As a result, battery charging may not be performed correctly.
Recently, wireless charging or non-contact charging technology has been developed and used for electronic devices, e.g., a mobile phone, to solve the above-mentioned problem.
The wireless charging technology uses wireless power transmission and reception which allows a battery to be automatically charged if the battery is positioned on a charging pad, i.e., without connecting a mobile phone which includes the battery to a separate charging connector. The wireless charging technology can improve the portability of the electronic devices because it does not require a wired charger.
The wireless charging technology can include an electromagnetic induction scheme which uses a coil, a resonance scheme which uses resonance, and an RF/microwave radiation scheme which converts electrical energy to a microwave energy and then transmits the microwave energy.
It is considered up to now that the electromagnetic induction scheme is mainstream.
A power transmission method through the electromagnetic induction includes transmitting electric power between a first coil and a second coil. When a magnet is moved in a coil, an induction current occurs. By using the induction current, a magnetic field is generated at a transmitting end, and an electric current is induced according to a change in the magnetic field so as to generate energy at a receiving end. The phenomenon is referred to as magnetic induction, and the power transmission method using magnetic induction has high energy transmission efficiency.
The resonance scheme includes a system in which electricity is wirelessly transferred using an electric power transmission principle of the resonance scheme based on a coupled mode theory. It is known that the resonant electrical energy does not affect surrounding machines or human bodies differently from other electromagnetic waves because the resonant electrical energy is directly transferred only to a device having a resonance frequency and unused parts are reabsorbed into an electromagnetic field instead of spreading into the air.
In order to sense a state where a wireless power receiving unit (PRU) is located on a wireless power transmitting unit (PTU), a method for detecting a change in the impedance of a power transmitter can be provided.
When the PTU detects the presence of a PRU through the detection of impedance change, the PTU may initiate communication with the PRU by supplying enough power to communicate with the PRU.
On the other hand, in a multi-charging state where one PTU charges a plurality of PRU, when a charging voltage for one PRU is excessively high or an exothermic reaction occurs, the PTU or PRU may experience a failure or may not charge normally.